Mr. Rodriguez, 54, was charged with murder in the Dec. 22, 2009, stabbing, but the jury of nine men and three women found him guilty of the lesser charge of voluntary manslaughter after just under 3-1/2 hours of deliberations.

Mr. Rodriguez, who was acquitted on a related charge of assault and battery with a dangerous weapon, is scheduled to be sentenced Friday. He faces a maximum sentence of 20 years’ imprisonment on the manslaughter conviction.

A first-degree murder conviction carries a mandatory sentence of life imprisonment without parole.

Mr. Jackson suffered a fatal stab wound to the chest in a makeshift basement apartment at 25 Charlton St.

The assault and battery with a dangerous weapon charge involved an allegation that Mr. Rodriguez held a knife to the throat of Tyrone Harris, who lived in the basement apartment and had invited Mr. Rodriguez there.

After repeatedly telling investigators he did not stab Mr. Jackson, Mr. Rodriguez eventually admitted doing so, but said he used the knife only after being attacked by Mr. Jackson and Mr. Harris. He said he and the other two men were high on crack cocaine at the time.

Mr. Harris, 47, testified during the five-day trial that Mr. Rodriguez took off his clothes, brandished a knife and indicated he wanted to have sex with a woman who was present shortly after his arrival at the apartment.

Mr. Harris said Mr. Jackson snatched the knife from Mr. Rodriguez and tossed it across the room. Mr. Rodriguez stabbed Mr. Jackson after recovering the weapon, according to Mr. Harris.

In his closing argument to the jury, defense lawyer John J. Roemer attacked the credibility of Mr. Harris.

“He is like the Kleenex box of lies. Pull out one, out pops another,” Mr. Roemer said.

Mr. Rodriguez’s lawyer cited Mr. Harris’s long criminal record, which includes a conviction for intimidation of a witness.

“That is a crime against the justice system. We expect truthfulness out of him when he’s fighting truthfulness in court?” Mr. Roemer asked.

He said Mr. Harris and Mr. Jackson had histories of violent behavior and told the jurors if they had reasonable doubt about whether Mr. Rodriguez acted in self-defense, they were obligated to find him not guilty.

Mr. Roemer also referred to the testimony of psychologist Paul A. Spiers, an expert witness for the defense, who said Mr. Rodriguez had limited intellectual capabilities and a history of depression, anxiety and alcoholism that could have affected his state of mind on the night of the killing.

“There was only one aggressor that night, only one person with a weapon. That was Felix Rodriguez,” Assistant District Attorney Brett F. Dillon said in his final summation.

“No one told you there was a fight beforehand except the defendant. Why? Because there wasn’t one,” the prosecutor told the jury.

Mr. Dillon said the evidence showed Mr. Rodriguez “sucker-punched” Mr. Jackson with a knife and argued that the fatal stabbing was both “deliberate and premeditated.”

He described Mr. Jackson’s slaying as “unnecessary and unprovoked.”

The jury began its deliberations shortly before 11:30 a.m. and reached its verdicts about 3:45 p.m.